Doesn't anyone here know how to help? I feel like I wanna hang myself

I have had this problem for a year or so and I have spent so long trying to fix it I feel like I am going to fucking cry.

I have the latest java and JDK. I can not run any .jar files. I can play stuff that uses java through my browser but cannot run a program off my hard drive. I am using vista.

Let me explain it in a simple form:

1. Father downloaded new java I think and maybe something else like windows update.
2. When I try to run my .jar files it says it doesnt know what to open it with.
3. Ages trying to fix it.
4. .jar files open a black command prompt box with text for a split second then it closes instantly.
5. uninstalled all my java staff again.
6. Reinstalled the newest Java and JDK.
7. See step 4.

1. Go to java installation directory, e.g c:\program files\java\jdk.......
2. Go to bin directory.
3. type java -jar c:\pathofthefile\nameofthefile.jar
basically, you are asking java to execute the specified jar file. java is the service that will execute your jar file. -jar is the option which tells java that target is a jar file. c:\pathofthefile\nameofthefile.jar is your jar file which you want to run.